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Exploitation and enhancement of the mechanical strain to modulate the magnetic properties are crucial for developing conformal wearable magnetic-electronic devices. However, the mechanical strain how to regulate the magnetic properties remains unclear for flexible thin film. Here, (111)-oriented SrRuO3 thin films are epitaxially grown on flexible mica substrates, and the influence of the mechanical bending on magnetic properties is studying by altering the curvature of the SrRuO3/BaTiO3/Mica heterostructure. The results show that the phase transition temperature does not reveal a significant dependence on both of convex and concave bending but they play a contrary role on the magnetic entropy change. Namely, the tensile stress (convex) increases the magnetic entropy change while the compressive stress (concave) decreases it. Moreover, based on the scale analysis method, we find that both bending states are directly correlated with the change of critical phase transition behavior. We think that the variation of domain wall configuration due to mechanical bending is the main reason for the change of magnetic properties. This study therefore not only identifies a strong magnetic property correlation in the mechanical strain, but also offers an avenue to improve flexible electronic devices with optimized performance.

Tricritical phenomenon appearing in multiple phases is a fundamental and attractive issue in condensed-matter physics. In this work, a field-modulated tricritical phenomenon is realized in single-crystal PrCu9Sn4. The magnetization under variable directions of field indicates strong magnetic anisotropy in PrCu9Sn4, which reveals ferromagnetic coupling for H//c. A paramagnetic-to-ferromagnetic magnetic transition occurs with H//c at T C = 11.7 K, which is evidenced to be of a first-ordered type. The systematical study of the critical behavior gives that β = 0.195(8), γ = 0.911(1), and δ = 0.0592(1) for H//c consistent with a tricritical mean-field model, which suggests a field-modulated tricritical phenomenon. A detailed H − T phase diagram around the tricritical point (TCP) is constructed for single-crystal PrCu9Sn4 for H//c, where ferromagnetic state, forced ferromagnetic phase and paramagnetic state meet at the TCP (H tr = 799 kOe, T tr = 11.3 K). The single-crystal PrCu9Sn4 supplies a platform to deep investigate the field-modulated magnetic couplings and tricritical phenomenon.

Large-scale growth of two-dimensional (2D) ferromagnetic thin films will provide an ideal platform for studying 2D magnetism and active spintronic devices. However, controllable growth of 2D ferromagnets over large areas faces tremendous challenges. Herein, we report a large-area growth of 2D ferromagnetic single-crystal thin films Cr4Te5 on Al2O3 (0001) substrates using pulsed laser deposition. X-ray diffraction patterns and atomic force microscopy detection confirm that all thin films have high quality epitaxy together with being atom-level smooth. Magnetic measurements show the persistence of ferromagnetic ordering state to above room temperature, with a Curie temperature ∼320 K, atomic magnetic moment ∼0.307 μ B /Cr, and the easy-magnetization axis in the film plane. Comparing with bulk Cr4Te5 single-crystal, the critical exponent β = 0.491 indicates that the magnetic interactions of the thin film obey the mean-field model rather than the 3D Heisenberg model. This work will open an avenue for growing large-scale 2D ferromagnets and developing room temperature 2D magnet-based nanodevices.

Ferroelectric with quantum-mechanical tunnel allows non-volatile resistance states and fast readout of the tunnel current in the ferroelectric tunnel junctions (FTJs) through the influence of ferroic orders. However, the complex interfacial effect between electrodes and traditional ferroelectric films has still remained to be solved. When 2D ferroelectrics are used in FTJs, the lattice-matched constraint and intermixing of cations between ferroelectric and substrate electrode can be avoid. Here we show various FTJs with low energy consuming, and high endurance made from 2D ferroelectric ReS2 and different electrodes such as Pt/ReS2/Au, W/ReS2/SiO2/Si and W/ReS2/Nb:STO. With the help of in situ atomic force microscopy and piezoresponse force microscopy, we show that the memory can be manipulated in less than 1 μm2 and the resistance switching should be caused by the ferroelectric polarization direction in the distorted ReS2. Then, we demonstrate that the memory devices can be easily transferred to a polyimide or flexible SiO2/Si substrate. These FTJs shows good bending stability, illustrating their potential applications in flexible electronics. Considering the weak Van der Waals interfacial bonding between 2D ferroelectric and electrode, the polarization-dependent Schottky emission and interface-limited Fowler–Nordheim tunnel current play the key role in resistance switching respectively. Our work provides a simple way to construct various building blocks for circuits in harsh electronics with low energy consuming, good bending stability and high-density data storage.

The atomic and electronic structures have been investigated for the multiferroic behavior in the perovskite oxides, which also can be tuned by oxygen vacancy for enhancing properties. Here epitaxial Sr(Ti0.875Fe0.125)O3-δ thin films were deposited on (001) SrTiO3 substrates by pulsed laser deposition and were post-annealed in an oxygen atmosphere. We found that the oxygen vacancies formed in high vacuum are the source of the macroscopic crystal distortion as the growth strain along out-of-plane. Moreover, it was determined that the full-filled Fe 3d states induced by oxygen vacancy effect are responsible for the decreased magnetization. This work demonstrates that the oxygen vacancy can both lead to atomic and electronic reconstructions in the perovskite films for manipulating ferroic properties.

The accurate band gap of 2.24 eV for hexagonal WO3 is obtained by adopting the revised Heyd-Scuseria-Ernzerhof screened hybrid functional. The large band gap is a result of the off-centered symmetry where the W atom forms two short and two long bonds with four neighboring in-plane O atoms. By adding/removing electrons into/from the crystal, the effect of charge doping is investigated. With introducing electrons, the off-centered symmetry gets weakened with a slight narrowing in band gap. However, the doping lifts the Fermi level into the conduction band, inducing an increase in transition energy for electrons. Similarly, the hole doping also results in a remarkable increase in the transition energy. Such band structure modulation can be used in high efficient photoabsorption, photocatalysis and surface-enhanced Raman spectroscopy.

The electronic and magnetic properties of BaTbO3 are studied by using the local-spin density approximation method where on-site Coulomb interaction U is included. The ground magnetic phase is found to be G-type antiferromagnetic with lattice constant of 4.278 A, which is consistent with experimental results. The states of Ba in the compound show obvious ionic characteristic, while very strong hybridization between Tb 4f and O 2p orbitals is found in the compound. The on-site Coulomb interaction U is found to have significant influences on the state distribution of Tb 4f. With the increase of U, most of the spin-up and spin-down states of Tb 4f move away from the Fermi level drastically, giving rise to the change of band gap of the compound and the variation of magnetic moment of Tb ions. The optimized value of U is determined to be 4.0 eV, and the corresponding band gap of BaTbO3 is 0.61 eV, which seems to be a narrow gap semiconductor rather than a good insulator.